Facilitators vs Sellers

Facilitators and sellers are two different roles in the x402 ecosystem.

Sellers

Sellers provide the API that can be purchased with x402 calls.

They typically put "x420 middleware" in front of their API which will reject a client's call with the "402 Payment Required" HTTP error code, detailing how much it costs, in which token, and on which network.

Processing this error code lets a client (like an agent, or a browser extension like Autopay) compose a cryptographic signature which allows the Facilitator to take this much money out of the client's account and send it to the Seller.

This process happens automatically. Sometimes, when a human is behind the wheel, a signature needs to be manually approved, but since x402 is mainly designed for agentic commerce, this is rare.

Facilitators

Facilitators are centralized services that provide a way for Sellers to get paid for their API offerings.

A facilitator accepts an authorization signature from a client (ERC3009 compliant), which allows it to take the balance of a token out of the client's account and send it to the payTo address specified by the Seller.

Sellers implement facilitators directly in their API middleware.

Software packages exist which allow a Seller to implement a range of facilitators at once on auto-failover or in round-robin style, so that is a faciliator is unavailable or low on gas, the API can automatically try using another one.